1. Field of the Invention
The present invention relates to a corrugated synthetic resin pipe including a pipe wall having a spirally corrugated shape, which is used, for example, as an underground drainage pipe or a sewage pipe, and also relates to a method for manufacturing the pipe.
2. Description of the Background Art
Conventionally, Hume concrete pipes have been used as underground drainage pipes and sewage pipes. In recent years, however, it has become popular to use corrugated synthetic resin pipes with a body having a substantially flat inner surface and an outer periphery having reinforcing projections spirally arranged thereon. The corrugated synthetic resin pipes are popular because they are as strong as and more durable, lighter in weight, and simpler in construction than Hume pipes. Two such corrugated synthetic resin pipes are connected to each other as follows. First, half joints each having a connecting flange are attached to the facing ends of the pipes with packing sheets set on the inner surfaces of the pipes. Next, the gaps between waterproof blocks and recesses are filled with caulking material. Then, the packing sheets are wound in a fully stretched condition around the pipes and fixed with a vinyl tape or the like. Finally, one half joint is put over the other, and then the flanges of the half joints are fixed to each other by bolts and nuts.
Such a connection structure, however, requires putting the upper and lower half joints, the packing sheets, the caulking material, and other parts together in the field in a specific procedure. This takes a lot of time and effort, thus decreasing the operating efficiency. It is also troublesome to manage the large number of component parts. Furthermore, it is a heavy burden for field workers to move two pipes to specific positions of the packing sheets after the packing sheets are laid on the inner surfaces of the half joints. In addition, the amount of the caulking material to be filled and the degree of stretching the packing sheets in the field vary between individuals, thus causing quality variations.
On the other hand, a new connection structure which makes the connection process easier and faster has been suggested (see, for example, Patent Document 1). In this connection structure, first, connecting flanges are welded to the facing ends of two corrugated synthetic resin pipes. Next, a packing is attached to a contact surface where the flanges are surface-contacted with each other, and finally, the flanges are fixed to each other by bolts and nuts. This connection structure provides higher workability and reliability than the conventional connection structure.
This connection structure, however, has the following problems. The connecting flanges, which are required to be connected using bolts and nuts, decrease operating efficiency. The pipe ends to which the flanges are welded can cause water leakage unless they are made watertight, and deformation of the flange surfaces can also cause water leakage. Avoiding the water leakage requires high quality in welding, and also in the strength, shape, and size of the flanges, which hinders cost reduction. Another problem is that the robust flanges, and the bolts and nuts to connect them inevitably increase the weight of the connected areas. Further another problem is that the connection between the flange surfaces via the packing limits the resistance to water and pressure of the flange surfaces, and requires evenly tightening bolts and nuts, which hinders improving operating efficiency.
Patent Document 1: Japanese Patent Unexamined Publication No. 2002-139178